The Anatomy of Viral DNA Molecules

Abstract

Without known exception, purifi ed virus particles, the virions, contain a single type of nucleic acid-RNA or DNA-never both. This fact provides the most convenient definition of a virus particle (115). The distinction be tween RNA-containing and DNA-containing viruses appears to be a pro found one that reflects a fundamental difference in their life cycle and evo lutionary origin. This review will be concerned with the DNA-containing viruses.It is generally a greed that viruses are reproduced from their own nu cleic acid. This can take place in various host cells whose biochemical ma chinery always provides substantial assistance in the process and sometimes even modifies the virus or its nucleic acid in a nongenetic way. These facts do not alter the idea that the identity and biological stability of viruses de pend solely upon the information in their own nucleic acids. In this regard they are like other microorganisms. To the extent that these generaliza tions are correct (and some unusual exceptions are known), a perfect un derstanding of the anatomy of viral DNA molecules, including the se quence of nucleotides, would define all tha,t can be known about the func tional potential of the virus. The term virus properly embraces all phases of the viral life cycle (35).Viral DNA molecules spend only part of their existence in mature virus particles called virions. They are found in infected cells, often in multiple copies and, in the case of temperate viruses, the viral DNA molecule is in corporated as a provirus into the DNA of the host cell. In this location it almost (but not quite) evades physical and chemical study, although the presence and the structure of prophage have been genetically studied for many years. It is a matter of reasonable expectation, and some faith, that a viral DNA molecule does not gain or lose information (nucleotide se quences) during any stage of its life cycle. In those cases where this does occur, the resulting entity must be considered a different, though related, virus.Relying on the notion that viral DNA molecules maintain their infor mational integrity at every stage of their life cycle, one may expect to ob tain information of general significance through the study of DNA mole-

Heat-stable and Density Mutants of Phages T1, T3 and T7

“…Unbroken DNA molecules were extracted by rolling equal volumes of purified phage suspension and freshly distilled water-saturated phenol on a test-tube roller with the tubes rotating about their long axis at 75 rev./min. The details of this method were described by MacHattie et al (1967). The extracted DNA was dialysed 4 to 5 times against a large excess of 0"05 M-NaC1, o.o~ M-tris, pH 8"0 to remove residual phenol and stored at 4 ° .…”

“…These phages were chosen because their DNA molecules, like those of T5, have non-permuted base sequences (Olligs, 1967;Thomas & MacHattie, 1967). It has been suggested that the maturation of phage DNA molecules in some cases involves the excision of phage-equivalent lengths of DNA from larger DNA structures known as concatemers (Streisinger, Emrich & Stahl, I967;Thomas, Kelly & Rhoades, 1968).…”

Bacteriophage T4 Genome

“…The packaging mechanism cuts the DNA when the head is filled, and it appears that EndoVII trims branches of DNA even after packaging has been initiated (523). The head full of DNA is about 3% longer than the genome size, accounting for the circular permutation of T4 genomes, with terminal redundancy of each genome; this circular permutation is the basis for the circular T4 genetic map (1048,1049,1073). Shorter or longer phage heads are occasionally formed, due to assembly errors that are increased by specific mutations in some head genes (256) or by incorporation of arginine analogues (194).…”

Lethality to leukemia cell lines of DNA interstrand cross-links generated by Cloretazine derived alkylating species

“…Hoechst 33258 was obtained from Molecular Probes, Inc., Eugene, OR. T7 DNA was employed because it is a long linear dsDNA of known size (37,900 bp; molecular weight 25 × 10 6 daltons) devoid of single-chain interruptions [16]. 90CE was synthesized as previously described [17].…”